1. Field of the Invention
The invention relates generally to lighting systems and particularly to an efficient, flat and transparent front-lighting system suitable for a wide range of applications such as illuminating automobile meters, road signs, reflective displays, shopping windows, high lighting pictures, jewelry, and art work. It also functions as a see-through lighting system for dentistry and surgery operation, medical and biological inspection tools, and many other applications. It is particularly suitable for precision work in which the conventional method of lighting from the side causes shadows and the parallax effect.
2. Description of the Related Art
The incandescent lamp and the fluorescent lamp are two of the most often used light sources for illumination, although some other light sources, such as light emitting diodes and electro-luminance, are often used for special applications such as indicators for electronic instruments. Most of the light sources, including the fluorescent lamp and the filament of the incandescent lamp are non-transparent. Some of the light sources, in particular, lamps based on gas discharge, such as neon lamps, are transparent when they are in an off state and do not emit light. These light sources, however, still can not be used as transparent, direct front-lighting systems since, when emitting light and placed between the viewer and the object, they will emit an equal amount of light directly towards the viewer and will therefore make it extremely difficult, if possible at all, to observe objects placed behind it. As a result, by using the conventional lighting method, objects are always being illuminated from the side with respect to the line of sight. Here, it should be noted that transparent objects are sometimes illuminated from the rear to achieve clearer viewing. The transmissive microscope is one example that uses backlighting to avoid parallax associated with side lighting for precision inspection.
A serious problem associated with the side illumination method is difficulty in observing detailed features of an object because of shadows and parallax effects. Small objects in deep holes in some medical inspection techniques as well as precision scientific and mechanical studies are particularly difficult to observe with side lighting. As an example, a dentist very often has to use a rather sophisticated lighting system and at the same time requiring that the mouth of a patient be stretched to the limit in order to observe teeth in detail. Another major problem associated with side illumination is the low energy efficiency. Because a relatively long distance between the light source and the object has to be maintained, an area much larger than the size of the object usually has to be illuminated with side lighting.
As will be seen hereinafter, with the transparent front-lighting system of the present invention, the lighting system can be placed directly on top of the object so that all of the light is effectively used for illuminating the object. Transparent direct lighting is particularly valuable for some molecular biomedical studies that use ultraviolet (UV) light to observe molecules labeled with a fluorescent material. The direct lighting approach of the present invention is not only highly efficient in its use of UV light from a lamp but also has the added advantage that the output UV light is directed toward the object and away from the observer so that the operator will not be exposed to excessive UV light irradiation which is harmful to the operator's health. It is possible to use a beam splitter (which transmits approximately 50% of light and reflects the other 50% ) for transparent direct front illumination. However, a sophisticated and bulky, optical arrangement requiring precision alignment is necessary for such an approach. A beam splitter based transparent front lighting system is, therefore, not widely used in practical application.